1. Field of the Invention
This invention relates to a kinematic mounting module for an optical element such as a lens, which allows the optical element to be moved from and replaced into a precisely defined position.
2. Description of Prior Art
In an optical system, such as spectroscopic apparatus, it is often required to remove a lens from the system and replace it with another lens in exactly the same position. The lens must be realigned each time and often the lens is in an awkward position which makes exchanging lenses difficult and time consuming. In addition, there is the danger of crashing into and damaging adjacent objects when replacing the lens in such a confined space. The same problem exists with other optical elements, such as mirrors and filters.
It is known to use a kinematic support arrangement to enable an object to be repeatably moved into and held in a precisely defined location. Such an arrangement is disclosed (though not in the field of mounting an optical element) in EP 0748669, in which a probe arm in a machine tool is movable in and out of a housing. Kinematic elements on a collar of the probe arm engage with further kinematic elements on an end plate of the housing to precisely define the operative position of the probe arm. Guide means guide the probe arm into its operative position, causing the collar to move towards the end plate along an axis orthogonal to their respective mating surfaces.
However this arrangement would sometimes not be suitable for repeatably positioning a lens in a precisely defined location in an optical system. The action of guiding the lens along the optical axis of the lens would have two main disadvantages. Firstly this arrangement would require a lot of space within the optical system and secondly, it would be difficult not to obstruct the optical path with the apparatus needed for this construction.
According to the present invention, an optical module which allows an optical element to be removed from and replaced into a predetermined position comprises:
a carrying member for carrying the optical element;
a receiving member for attachment to the optical system for receiving the carrying member;
mutually engageable locating elements on the carrying member and on the receiving member respectively, said elements co-operating with each other when engaged to constrain the degrees of freedom of the carrying member kinematically, thereby precisely defining the predetermined position; and
guide means for guiding the carrying member into a position in the receiving member in which the locating elements are engaged with each other.
Preferably the optical element has an optical axis, and the guide means guides the carrying member into its position in the receiving member in a direction transverse to the optical axis.
The optical element may be a lens.
Reference should be made to U.S. Pat. No. 5,446,970 for a discussion of one meaning of the terms xe2x80x9ckinematicxe2x80x9d, xe2x80x9ckinematicallyxe2x80x9d and like terms, as used in this specification. These terms encompass not only kinematic supports in which point contacts are provided between the respective pairs of elements on the carrying and receiving members, but also semi- or quasi-kinematic supports, in which there are small areas or lines of contact between the respective elements.